1. Field of the Invention
This invention relates generally to a system and method for managing the commanded engine torque and motor torque for a hybrid electric vehicle and, more particularly, to a system and method for determining the commanded engine torque and motor torque that minimizes fuel consumption and manages battery state of charge in a hybrid electric vehicle.
2. Discussion of the Related Art
Hybrid electric vehicles use an engine and one or more electric motors to propel the vehicle to achieve better fuel economy and lower emissions than conventional vehicles. The engine output power does not have to equate power demands as in conventional vehicles. Generally the engine is used at high load demands and the motor is used at low load demands. A combination of both engine power and electric motor power can also be provided for increased performance purposes. The electric motor supplements the power from the engine when the engine cannot efficiently cope with the current power demands. The motor can absorb the engine power and store it in a motor battery for later use. The engine can also be used to recharge the battery during prolonged use of the motor.
The battery state of charge (SOC) is an important consideration when determining if the motor should be used because a battery is more efficient if the battery state of charge is between an upper bound battery charge and a lower bound battery charge. The battery also needs to be self-sustaining. Therefore, it is desirable to try and maintain the battery state of charge at or near a nominal value.
Known hybrid electric vehicles can be improved by better determining when to use engine power, electric power or a combination of both to increase the fuel economy and lower the vehicle emissions.